Bis-p-Sulfonatocalix[4]arene-Based Supramolecular Amphiphiles with an Emergent Lower Critical Solution Temperature Behavior in Aqueous Solution and Hydrogel

Green-step assembly of the supramolecular amphiphile constructed by sodium carboxymethyl cellulose and calixarene for facile loading of hydrophobic food bioactive compounds

The use of biologically active compounds is often limited due to their poor aqueous solubility, which generally reduces their bioavailability and useful efficacy. In this regard, a wide search is currently underway for colloidal systems capable of encapsulating these compounds. In the creation of colloidal systems, long-chain molecules of surfactants and polymers are mainly used, which in an individual state do not always aggregate into homogeneous and stable nanoparticles. In the present work, cavity-bearing calixarene was used for the first time to order polymeric molecules of sodium carboxymethyl cellulose. A set of physicochemical methods demonstrated the spontaneous formation of spherical nanoparticles by non-covalent self-assembly contributed by macrocycle and polymer, and formed nanoparticles were able to encapsulate hydrophobic quercetin and oleic acid. The preparation of nanoparticles by supramolecular self-assembly without use of organic solvents, temperature and ultrasound effects can be an effective strategy for creating water-soluble forms of lipophilic bioactive compounds.

Multifunctional Host Polymers Assist Au Nanoclusters Achieve High Quantum Yield and Mitochondrial Imaging

The high biocompatibility and excellent photostability of Au nanoclusters (AuNCs) make them stand out in the bioimaging of nanoparticles. However, the low quantum yield and inferior targeting ability of water-soluble AuNCs greatly limit their biological applications. In this study, we designed and synthesized multifunctional host polymers PolySC₄AP and FGGC@AuNCs to fabricate PolySC₄AP/FGGC@AuNC assemblies via a host-guest interaction based on SC₄ (sulfonatocalix[4]arene) and positively charged FGGC ligands (phenylalanine-glycine-glycine-cysteine). Owing to the host-guest assembly strategy and rigid polymer matrix, the quantum yield of FGGC@AuNCs was significantly promoted from 7.0 to 35.3%, accompanied by considerable morphological changes of FGGC@AuNCs. Moreover, PolySC₄AP/FGGC@AuNCs could monitor the location of mitochondria along with R (Pearson's correlation coefficients) value for the co-localization as high as 0.9605, which provided a novel strategy for targeted bioimaging with luminophore.

An amphiphilic water-soluble biphen[3]arene with a tunable lower critical solution temperature behavior

The first amphiphilic water-soluble thermoresponsive biphen[3]arene with a tunable lower critical solution temperature behavior is reported.

Stimuli-Responsive Polymers with Room-Temperature Phosphorescence

Taking advantages of the impressing behaviors of room-temperature phosphorescence (RTP), the explorations in RTP materials are not only limited to efficient emission and ultralong lifetime of phosphorescence. The discovery and creation of stimuli-responsive properties have become the major pursuit, which will lay a solid foundation for future applications in RTP materials. Based on this, a review centered on recent progress of stimuli-responsive RTP materials is summarized to show frontier development in polymer systems. Different kinds of stimuli-responsive factors including light, oxygen, temperature, mechanical force and pH regulations are investigated in this review. Many potential applications and promising strategies are deeply discussed with the hope to assist future studies in this area.

Re-entrant Photoinduced Morphological Transformation and Temperature-Dependent Kinetic Products of a Rectangular Amphiphilic Diarylethene Assembly

An amphiphilic rectangular-shaped photochromic diarylethene bearing two hydrophobic alkyl chains and two hydrophilic tri(ethylene glycol) chains was synthesized, and its photoinduced morphological transformation in water was investigated. Two unexpected phenomena were revealed in the course of the experiments: a re-entrant photoinduced macroscopic morphological transformation and temperature-dependent kinetic products of supramolecular assembly. When the pure closed-ring isomer was dispersed in water, a re-entrant photoinduced morphological transformation, that is, a photoinduced transition from the hydrated phase to the dehydrated phase and then back to the hydrated phase, was observed by optical microscopy upon irradiation with green light at 20 °C; this was interpreted by the V-shaped phase diagram of the LCST transition. The aqueous assembly of the pure closed-ring isomer was controlled by changing the temperature; specifically, rapid cooling to 15 and 5 °C gave J and H aggregates, respectively, as the kinetic products. The thermodynamic product at both temperatures was a mixture of mostly H aggregate with a small amount of J aggregate. This behavior was rationalized by the temperature-dependent potential energy surface of the supramolecular assembly.

A facile way to obtain near-infrared room-temperature phosphorescent soft materials based on Bodipy dyes

Research on pure organic room-temperature phosphorescent (RTP) materials has made great advances but near-infrared (NIR) RTP emitting materials are still rare. Novel amorphous acrylamide copolymers containing iodine substituted borondipyrromethene (Bodipy) were prepared to obtain strong absorption in the visible region and moderate RTP in the NIR region with much larger Stokes shift than the fluorescence emission of traditional Bodipy dyes. Expensive metals and crystallization were left out to avoid biotoxicity and strict preparation conditions. Monoiodo and diiodo-Bodipy derivatives were both designed to study the substitution effect of iodine atoms. Photophysical properties, phosphorescence quantum yield and lifetime were characterized. Gels with NIR RTP emission were facilely prepared with the incorporation of ureidopyrimidone (UPy) and N,N'-methylenebisacrylamide (MBAA). The mechanical properties of the gels were measured using a rheometer and the results showed that the gels displayed fast self-healing ability due to the strong quadruple hydrogen bonding between UPy moieties.

Photoinduced repetitive separation of a supramolecular assembly composed of an amphiphilic diarylethene mixture

A supramolecular assembly composed of a two-component mixture of amphiphilic diarylethenes, which have octyloxycarbonyl and N-octylcarbamoyl groups, showed a unique macroscopic transformation upon irradiation with UV light and subsequent standing in the dark. Unlike the pure compounds, the assembly was repetitively separated into a blue sphere and a red-purple sparse structure. Both the blue sphere and the sparse structure turned into colorless spheres upon irradiation with visible light and the divided colorless spheres showed the same response to UV and visible light. Phase diagrams based on the change in absorption spectra upon temperature change suggested that the transformation originates from a LCST transition. In the 0.5 : 0.5 mixture, in contrast to the pure compounds, the transition temperature sharply changed at around 50% of the fraction of the closed-ring isomer. TEM imaging showed that the 0.5 : 0.5 mixture with high photoisomerization yield formed a 10 nm-sized network. Judging from the phase diagram and TEM images, the separation is understood as the local phase transition of the regions with a high fraction of the closed-ring isomer.

Multiple threading of a triple-calix[6]arene host

The synthesis of the triple-calix[6]arene derivative 6 in which three calix[6]arene macrocycles are linked to a central 1,3,5-trimethylbenzene moiety is reported. Derivative 6 is able to give multiple-threading processes in the presence of dialkylammonium axles. The formation of pseudo[2]rotaxane, pseudo[3]rotaxane, and pseudo[4]rotaxane by threading one, two, and three, respectively, calix-wheels of 6 has been studied by 1D and 2D NMR, DOSY, and ESI-FT-ICR MS/MS experiments. The use of a directional alkylbenzylammonium axle led to the stereoselective formation of endo-alkyl pseudo[n]rotaxane stereoisomers.

LCST phase behavior of benzo-21-crown-7 with different alkyl chains

The introduction of hydrophobic units into crown ethers can dramatically decrease the critical transition temperature of LCST and realize macroscopic phase separation at low to moderate temperature and concentration. Minor modifications in the chemical structure of crown ethers (benzo-21-crown-7, B21C7s) can effectively control the thermo-responsive properties.

A degradable low molecular weight monomer system with lower critical solution temperature behaviour in water

A degradable thermo-responsive system was prepared and investigated. The degradation behaviour induced by the cleavage process of the thermo-sensitive crown ethers effectively altered the thermo-responsiveness.

The light-controlling of temperature-responsivity in stimuli-responsive polymers

Light-controlling of phase separation in temperature-responsive polymer solutions by using light-responsive materials for reversible controlling physical and chemical properties of the media with an out-of-system stimulus with tunable intensity.

Construction of Metallacage-Cored Supramolecular Gel by Hierarchical Self-Assembly of Metal Coordination and Pillar[5]arene-Based Host-Guest Recognition

In this work, a Pd₂ L₄ metallacage 2•([BF₄ ]^- )₄ with four pillar[5]arene units is first prepared and characterized by 1D multinuclear NMR (¹ H, ¹¹ B, and ¹⁹ F NMR), 2D ¹ H-¹ H correlation spectra, ¹ H-¹³ C heteronuclear single quantum coherence, and diffusion-ordered NMR spectroscopy, and electrospray ionization time-of-flight mass spectrometry. By the introduction of a ditopic guest molecule 3 into a chloroform solution of 2•([BF₄ ]^- )₄ , a supramolecular polymer network gel is successfully constructed based on the metal coordination interactions and host-guest recognition between the pillar[5]arene units of 2•([BF₄ ]^- )₄ and neutral ditopic guest molecule 3. The temperature and pH responsivenesses of the supramolecular gel are studied, which are further employed for the controlled release of different cargos. As a demonstration, emodin and methylene blue are trapped in the cavities of the metallacage and in the pores of the supramolecular gel, respectively. Methylene blue is first released along with the gel-sol transition while emodin is then released by the further addition of acid to destroy the metallacage. This study explores the use of metallacage-cored supramolecular network gels for sequential controlled release and contributes to the development of smart and adaptive materials.

Supramolecular control over pillararene-based LCST phase behaviour

Based on the supramolecular interactions between pillar[5]arenes and ionic liquids, supramolecular control was successfully introduced into thermo-responsive systems to adjust LCST phase behaviour in water.

Substituent effect on the dynamics of the inclusion complex formation between protoberberine alkaloids and cucurbit[7]uril

The dynamics and activation parameters of alkaloid entry into and exit from cucurbit[7]uril significantly depend on the substitution pattern.

A photo-responsive macroscopic switch constructed using a chiral azo-calix[4]arene functionalized silicon surface

A photo-responsive macroscopic switch was fabricated using a chiral azo-calix[4]arene derivative (FC4AD) functionalized silicon surface and exhibited selective and reversible recognition of (1R,2S)-1-amino-2-indanol through the variation of wettability.

Phototransformative Supramolecular Assembly of Amphiphilic Diarylethenes Realized by a Combination of Photochromism and Lower Critical Solution Temperature Behavior

Amphiphilic diarylethenes bearing octyloxycarbonyl and N-octylcarbamoyl groups have been designed and synthesized. These ester- and amide-linked compounds form micrometer-sized supramolecular assemblies in water, and these assemblies exhibit photoinduced macroscopic morphological transformations upon alternate irradiation with UV and visible light. The ester-linked diarylethene showed a transformation between colorless spheres and a red-purple hazy fringe, whereas the microspheres of the amide-linked diarylethene showed changes in color, size, and shape, but the spheres did not show division. TEM images revealed that the spheres of the open-ring isomers have coacervate structures, with bicontinuous aqueous and organic phases. The closed-ring isomers of the ester- and amide-linked compounds were found to form nanofibers and thin layers, respectively. These compounds showed absorption spectral shifts at temperatures corresponding to the lower critical solution temperature (LCST) transition. This morphological transformation can be rationalized as the photoinduced phase transition between the high- and low-temperature phases of the LCST transition. These results open up a new avenue for the design of phototransformative supramolecular assemblies based on a combination of photochromism and LCST behavior.

Cationic Supramolecular Hydrogels for Overcoming the Skin Barrier in Drug Delivery

A cationic bis-imidazolium-based amphiphile was used to form thermoreversible nanostructured supramolecular hydrogels incorporating neutral and cationic drugs for the topical treatment of rosacea. The concentration of the gelator and the type and concentration of the drug incorporated were found to be factors that strongly influenced the gelling temperature, gel-formation period, and overall stability and morphology. The incorporation of brimonidine tartrate resulted in the formation of the most homogeneous material of the three drugs explored, whereas the incorporation of betamethasone resulted in a gel with a completely different morphology comprising linked particles. NMR spectroscopy studies proved that these gels kept the drug not only at the interstitial space but also within the fibers. Due to the design of the gelator, drug release was up to 10 times faster and retention of the drug within the skin was up to 20 times more effective than that observed for commercial products. Experiments in vivo demonstrated the rapid efficacy of these gels in reducing erythema, especially in the case of the gel with brimonidine. The lack of coulombic attraction between the gelator-host and the guest-drug seemed particularly important in highly effective release, and the intermolecular interactions operating between them were found to lie at the root of the excellent properties of the materials for topical delivery and treatment of rosacea.

Smart Fluorescent Nanoparticles in Water Showing Temperature-Dependent Ratiometric Fluorescence Color Change

We synthesized two different amphiphilic small molecules 1 and 2 by attaching the same oligo(ethylene glycol) (OEG) unit to the same dicyanodistyrylbenzene (DCS) fluorophore but at different positions. These molecules self-assemble into nanoparticles in water and show lower critical solution temperature (LCST) at 26 and 58 °C, respectively. Upon heating, the transition of hydrophilic coils to hydrophobic globules of the OEG unit leads to the change in the stacking structure of the luminescent DCS cores. As a result, it shows significant ratiometric fluorescence color changes from excimeric yellow emission to monomer-dominated green emission. Interestingly, the coassembly of 1 and 2 exhibits single transition temperature between the transition temperatures of the two components. Moreover, it is demonstrated that the transition temperature of the coassembly is delicately tuned over 26-58 °C by varying the molar mixing ratio of them.

Kinetics of the reversible inclusion of flavopereirine in cucurbit[7]uril

The temperature dependence of the formation and dissociation kinetics of the flavopereirine–cucurbit[7]uril complex is revealed.

Reversible switching of a supramolecular morphology driven by an amphiphilic bistable [2]rotaxane

A supra-amphiphilic [2]rotaxane-based switch could self-assemble into spherical vesicles in aqueous solution and transform into worm-like micelles in a basic environment.

Cu(II) Ion-Responsive Self-Assembly Based on a Water-Soluble Pillar[5]arene and a Rhodamine B-Containing Amphiphile in Aqueous Media

Cu(II) ion-responsive self-assembly in aqueous media was achieved based on a water-soluble pillar[5]arene host and a rhodamine B-containing amphiphile guest. The host-guest complex acted as a supra-amphiphile and self-assembled into vesicles. After addition of Cu(II), vesicles turned into solid nanoparticles, accompanied by the color change of the solution from colorless to red and a fluorescence "on" phenomenon.

Perylene bisimide hydrogels and lyotropic liquid crystals with temperature-responsive color change

The self-assembly of perylene bisimide (PBI) dyes bearing oligo ethylene glycol (OEG) units in water affords responsive functional nanostructures characterized by their lower critical solution temperature (LCST). Tuning of the LCST is realized by a supramolecular approach that relies on two structurally closely related PBI-OEG molecules. The two PBIs socially co-assemble in water and the resulting nanostructures exhibit a single LCST in between the transition temperatures of the aggregates formed by single components. This permits to precisely tune the transition from a hydrogel to a lyotropic liquid crystal state at temperatures between 26 and 51 °C by adjusting the molar fraction of the two PBIs. Owing to concomitant changes in PBI-PBI interactions this phase transition affords a pronounced color change with "fluorescence-on" response that can be utilized as a smart temperature sensory system.

Effect of Macrocycle Size on the Self-Assembly of Methylimidazolium Surfactant with Sulfonatocalix[n]arenes

The effect of macrocycle size on the association of supramolecular amphiphiles composed of 4-sulfonatocalix[n]arene and 1-methyl-3-tetradecylimidazolium (C₁₄mim⁺) was studied in aqueous solutions at pH 7. When the cavitand contained four sulfonatophenol units (SCX4), formation of spherical nanoparticles (NPs) was observed. By contrast, both supramolecular micelle (SM) and NP formation could be attained in the presence of NaCl when the larger, more flexible 4-sulfonatocalix[8]arene (SCX8) served as the host compound. The SCX8-promoted self-assembly into the SM was enthalpically more favorable than the NP production, but the molar heat capacity changes in the two processes barely differed. An addition of 50 mM NaCl significantly increased the enthalpy of C₁₄mim⁺-SCX8 NP formation, thereby making the self-organization into the SM more favorable. The transformation of SM into NP at high temperatures was due to the substantial entropic contribution to the driving force behind the NP formation. The critical micelle concentration (cmc) and the local polarity in the headgroup domain were considerably lower for the SM compared with those of the conventional C₁₄mim⁺Br^- micelle.

p-Sulfonic acid calix[4]arene-functionalized alkyl-bridged organosilica in esterification reactions

Two new p-sulfonic acid calix[4]arene- and p-sulfonic acid calix[6]arene-functionalized organosilica have been synthesized using a sol–gel method and applied as heterogeneous catalysts in esterification reactions.